Mary Quinn is asked to take on one more case for the Agency, to watch for the return of Mrs. Thorold, whose husband is dying in jail and who has a grudge against Mary's fiance and partner in crime-solving, James Easton.
Hesitating to accept James' marriage proposal out of fear of losing her independence, Mary watches over a dying prisoner whose wife holds a grudge against James, at the same time a familiar Chinese prizefighter arrives in London.
